Spinal cord ischemia : An experimental study of the spinal cord blood supply and peroperative ischemia detection by a new method of intrathecal monitoring

Abstract: Spinal cord ischemia associated with thoracoabdominal aortic surgery may lead to devastating neurological complications. Improvement in bypass techniques and various adjunctive measures has reduced its incidence, but still 5-10 % of the patients develop postoperative paraplegia. There is no universally accepted method for the detection of spinal cord ischemia. Intraoperative monitoring methods are important for the prediction of ischemia and guidance in aorticreplacement strategy. This thesis presents a new technique for continuous peroperative monitoring of intrathecal oxygenation.A multiparameter sensor was used to measure cerebrospinal fluid (CSF) PO2, PCO2 and pH during thoracic aortic cross-clamping in pigs. The findings were experimentally validated by comparisons with epidural laser-Doppler flowmetry and with morphological outcome, as assessed by electron microscopy of immersion fixated spinal cord specimens. The CSF monitoring was used to study functional aspects of segmental and collateral spinal cord blood supply. An experimental model was developed for the study of selective spinal cord ischemia. For this purpose a passive aortic shunt was used.The new monitoring method correlated in the experimental situation with measurements of microcirculation and changes in spinal cord ultrastructure associated with aortic cross-clamping. It proved to be sensitive for detecting ischemia and responded rapidly to alterations in spinal cord circulation. The confounding hemodynamic effects of cross-clamping and systemic reperfusion injuries to the spinal cord could be avoided in the selective ischemia model. The shunt model was also used to study the beneficial effects of hyperoxemia during spinal cord hypoperfusion. In conclusion, this thesis presents a new monitoring method for spinal cord oxygenation during experimental aortic occlusion. The thin flexible sensor can be used percutaneously in humans and comparative studies are needed to correlate the findings with neurophysiological evaluations and clinical outcome.